Histological differentiation between chlamydial and bacterial epididymitis: nondestructive and proliferative versus destructive and abscess forming--immunohistochemical and clinicopathological findings.

Chlamydia trachomatis (CT) and Escherichia coli (EC) antigens were sought in routinely prepared paraffin-embedded sections from 31 cases of acute and chronic epididymitis by indirect immunoperoxidase staining. Chlamydia trachomatis antigens were detected in epithelial cells as cytoplasmic inclusions in samples from six patients (mean age, 43 years) with severe epididymitis, characterized by minimally destructive, periductal, and intraepithelial inflammation with active epithelial proliferation. Squamous metaplasia and formation of lymphoepithelial complexes occasionally were noted. Escherichia coli antigens, common to other pyogenic bacteria, were observed in the cytoplasm of foamy histiocytes in samples from seven patients (mean age, 60 years), characterized by highly destructive epididymitis forming large abscesses and xanthogranulomas. Specimens from 18 patients were negative for either antigen. Pre-embedding immunoelectron microscopy on paraffin-embedded sections demonstrated positive reactions on the cell wall of the chlamydial bodies and rod-shaped bacteria. Escherichia coli-positive cases were accompanied by scrotal pain, pyuria, positive bacterial culture, leukocytosis, accelerated erythrocyte sedimentation rate, and a positive C-reactive protein test. Chlamydia trachomatis-positive cases were clinically indolent and manifested by an epididymal tumor. Chlamydial epididymitis can be distinguished from bacterial epididymitis not only clinically and immunohistochemically but also histologically.